Add support for Fedora 20 to nodepool

For TripleO, one of our test cases is a fully Fedora-driven test,
this adds support for Fedora as a nodepool VM by adding support
to prepare node scripts.

Also adding install_devstack_dependencies.sh for Ubuntu and Fedora
shared dependencies for DevStack (and TripleO) preparation scripts.

Change-Id: I7399cc4d4b6ec6f8598afa68bc99ebb24cb01f64
Merge "Add support for Fedora 20 to nodepool"